Alien Hominid Invasion

This one is hard to pull off but with the right weapon and level set up it is doable

WEAPON

First thing we'll want do is make a build with the highest DPS we can. You may have to hit a hideout and spin for better gear as it's all RNG what you'll have to work with. I found the Human Mini gun worked the best for me, my set up was
Human Minigun lvl10 (+19% fire rate)
Boost 1 lvl9 (Range +28% Clip size +40% -72% dig)
Boost 2 lvl10 (Def +11% Reload speed +16% -12% crit)
Head lvl9 (DMG +9% Triple Bullet +14% -1 live cap)
Mutation Weapon Specialist (reload +7% clip size +14%)

I found the faster rate of fire/ reload speed with the larger clip size allowed me to fire almost continuously, but you could also make a build around double/triple bullet with crit on hit % up and faster rate of fire to deal more damage but reloading more often. Piercing shot +2 with rate of fire and dmg up is also a good option to hit multiple enemies at once. There are probably better DPS builds, I was just working with what I had at the time.

LEVEL

Now that we have our DPS load out next we need to keep an eye out for a city block that has the three base agents side by side icon on top of it (This icon means more agents spawn in as hazards for this level after the 5 minute mark). You may have to beat a few levels to get to one like this as the sometime appeared mid map. Play the level but don't complete a task, just stay at the start and kill/ survive for the first 5 minutes. Once the hazard level goes off try not to kill any normal agents, just take out armor or big shield guys as they'll get in the way. Now just run back and forth in a small area to get the agents to bunch up, you can also ride their heads to bring them closer to each other. Once you notice you have 10 or more agents all together unload on them and the achievement should be yours!

TIP - When you load into the level try to run around and see if Kid Boost is on the level, he will have one of three power ups. The one you want looks like an orange (!) this will raise clip size, fire rate, damage and triple bullet chances for a short time. If it is there use it right before you attempt to kill 10 agents.

TIP - If you're on your last life before you get the achievement quitting to menu and loading up the game puts you back right before you started the level so you can try again. **When playing solo offline**
This trick can also be used to get the right kid boost on the level.

This one kinda just happened. My only words of advice is to use stuff that would hit mutable enemies at once: Fire running ability, Grenade, Missel launcher, Bee cannon, Laser beam.